In the field of converting hydraulic energy into mechanical or electrical energy, it is known to use a hydraulic machine such as a turbine, a pump or a pump-turbine. In turbine mode, the machine drives a shaft in rotation, thus transforming hydraulic energy into mechanical energy. This energy conversion is achieved by means of a runner having a runner crown, a runner band and blades which are distributed about the axis of rotation of the runner, between the runner crown and the runner band. The blades extend, following a curved line, between a first edge and a second edge which are respectively, in operation, a leading edge and a trailing edge for the flow of water. When operating in turbine mode, the water flows from an upstream water reservoir, through a penstock and arrives in a casing surrounding the runner of the machine. The casing then distributes the water between the blades of the runner. The blades have a specific profile by means of which regions of low pressure can be created inside the runner. This causes the runner to rotate. When the water reaches the trailing edge of the blades, it moves toward a downstream draft tube.
One of the current recurring issues in the field of hydraulic machines is the production of a Kármán vortex street close to and downstream of the trailing edges of the blades of the runner. More precisely, the trailing edges of the blades of the runner are not very streamlined and produce a periodic pattern of vortices caused by the unstable separation of the flow around the blades. The Kármán vortex streets reduce the efficiency of the machine and represent a dynamic load on the blades, which can lead to cracks.
The production of a Kármán vortex street is greater the thicker the trailing edge of the blade. A first solution is therefore to reduce as far as possible the thickness of the trailing edge in an asymmetric manner so as to disrupt the symmetry of the phenomenon, and the intensity thereof. This approach does make it possible to reduce the Kármán vortex streets, but cannot eliminate them as the properties of the steels used do not allow the necessary reduction in thickness.